Doors do not provide adequate protection against burglars if a lock can be forced or broken by prying the door open in the vicinity of the lock. This invention provides an ordinary apartment or house door with bolts that extend from different edges of the door, and from all edges in the preferred construction, so that the door cannot be opened even though the pins on the hinges are removed and even though tools are used to pry the edge of the door at the edge which is remote from the hinges. Prying the door along other edges does not have any effect on making the door swing on its hinges.
It is a common practice to have multiple bolts on the doors of bank vaults, but these are extremely complicated and expensive doors and completely unsuitable for use in an apartment or a house. This invention provides multiple bolts and it is difficult to operate multiple bolts without substantial mechanical advantage. Theoretically, the door knob might have a crank which could be rotated to turn gearing in order to gain the mechanical advantage manually; but it is more practical to utilize a small electric motor and to obtain the mechanical advantage by gearing. In order to obtain a simple and relatively inexpensive mechanism, the door is hollow and has the bolts which project from the edges of the door connected within the door to four arms which are disposed at 90.degree. to one another. These arms are connected with a common hub, a portion of which is a segment of a gear and meshes with a driving gear at one end of a transmission which reduces speed and increases power of a motor connected with the other end of the transmission. The hub also has cam mechanism for operating a switch to stop the motor when the bolts complete their movement into projected or retracted positions. Rotating a door knob or other switch will operate the motor in a direction to lock the door; but the door cannot be unlocked without operating another swtich which can be controlled by a key; but is preferably controlled by a coded magnetic card, such as used by many of the banks for dispensing limited sums of money to depositors when the bank is closed. The slot or keyhole of this key switch is accessible from outside the door, but the door can be opened from the inside by another swtich which bypasses the key switch.
Another feature of the invention provides for automatic unlocking of the door in the event that the apartment or house catches fire and the inside switch for unlocking the door may not be accessible to occupants of the apartment or house. This safety fire switch is operated by a thermostat if the room in which it is located becomes hot.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.